I bought an old Trek off Ebay and it is a steel frame. The serial number is T2KB75269 With a 7 just under the 9. I can't find anything on serial numbers. Is there a place I can go to find out what it is. I asked a bike shop and they said probably late 70's early 80's. It has a newer seat. 21 gears. Mountain bike handle bars and 700 tires and wheels. By this I think someone customized it over the years for their self. Thanks for any help you can give.